Image forming apparatus

ABSTRACT

An image forming apparatus includes first and second devices selectively operable for developing an electrostatic latent image on a photosensitive member, toner accommodating devices for accommodating developer, detecting devices for detecting toner density in each of developers, a judging device for judging whether the first and second developers have same color, a selecting device responsive to the detecting device and judging device for automatically selecting the second developing device in the case where the toner density in the first developer is less than a specified value and where the toner density in the second developer is not less than the specified value under the judgment by the judging device that the first and second developers have same color, replenishing devices for replenishing toner to each of the first and second developers, and means for activating the replenishing device so as to continuously replenish toner to the first developer until the toner density therein reaches the specified value in the case where both of the toner density in the first and second developers are less than the specified value even if the first and second developers have same color, while prohibiting an image forming operation.

BACKGROUND OF THE INVENTION

The present invention generally relates to an image forming apparatus inwhich a plurality of developing devices are arranged.

Conventionally, an image forming apparatus is known in which a pluralityof developing devices selectively operable for developing electrostaticlatent image are arranged at a side of an electrostatic latent imagesupport member. In the apparatus, since toner in the developing devicesis consumed by development, replenishment of toner corresponding toconsumption of toner must be suitably performed.

However, when documents having much solid portion are continuouslycopied, amount of consumed toner per one copying operation is extremelylarge. Therefore, although replenishment of toner is performed, densityof toner in the developer in using is lower than a required level,resulting an image on a copied paper sheet in poor quality. Furthermore,when the apparatus has such function that copying operation is stoppedto wait during density of toner reaches the required level, the waitingtimer period is long and it is necessary for next copying operation towait for a long time.

SUMMARY OF THE INVENTION

Accordingly, an essential object of the present invention is to providean image forming apparatus in which a waiting time period is less thanbefore and many documents can be copied in a short time while keepingimages of copied papers in good quality.

In accomplishing this and other objects, there is provided an imageforming apparatus in which an electrostatic latent image formed on aphotosensitive member is developed by a developer incorporating tonerand carrier and subsequently transferred to a paper, the apparatuscomprising: first and second developing means selectively operable fordeveloping the electrostatic latent image by first and seconddevelopers, respectively; toner accommodating means for accommodatingtoner to be replenished to each of the developers; detecting means fordetecting toner density in each of the developers; judging means forjudging whether the first and second developers have same color;selecting means responsive to said detecting means and judging means forautomatically selecting said second developing means in the case wherethe toner density in the first developer is less than a specified valueand where the toner density in the second developer is not less than thespecified value under the judgment by said judging means that the firstand second developers have same color; replenishing means forreplenishing toner to each of the first and second developers; and meansfor activating said replenishing means so as to continuously replenishtoner to the first developer until the toner density therein reaches thespecified value in the case where both of the toner density in the firstand second developers are less than the specified value even if thefirst and second developers have same color, while prohibiting an imageforming operation.

In another aspect of the present invention, an image forming apparatusin which an electrostatic latent image formed on a photosensitive memberis developed by a developer incorporating toner and carrier andsubsequently transferred to a paper, the apparatus comprising: first andsecond developing means selectively operable for developing theelectrostatic latent image by first and second developers, respectively;toner accommodating means for accommodating toner to be replenished toeach of the developers; detecting means for detecting toner density ineach of the developers every image forming operation; first replenishingmeans responsive to said detecting means for replenishing apredetermined amount of toner from said respective toner accommodatingmeans to the respective developer when the toner density detected bysaid detecting means is less than the specified value; means forcounting the continuous number of replenishment by said firstreplenishing means; second replenishing means responsive to saidcounting means for continuously replenishing toner from said toneraccommodating means to the respective developer until the toner densityreaches the specified value when the continuous number of replenishmentby said second replenishing means becomes a predetermined number; andmeans for prohibiting an image forming operation during replenishment bysaid second replenishing means.

In a further aspect of the present invention, an image forming apparatusin which an electrostatic latent image formed on a photosensitive memberis developed by a developer incorporating toner and carrier andsubsequently transferred to a paper, the apparatus comprising: first andsecond developing means selectively operable for developing theelectrostatic latent image by first and second developers, respectively;toner accommodating means for accommodating toner to be replenished toeach of the developers; detecting means for detecting toner density ineach of the developers every image forming operation; first replenishingmeans for replenishing a first predetermined amount of toner to therespective developer when the toner density detected by said detectingmeans is not less than a specified value; second replenishing meansresponsive to said detecting means for replenishing a secondpredetermined amount of toner more than said first one to the respectivedeveloper when the toner density detected by said detecting means isless than the specified value; means for counting the continuous numberof replenishment by said second replenishing means; third replenishingmeans responsive to said counting means for continuously replenishingtoner to the respective developer until the toner density reaches thespecified value when the continuous number of replenishment by saidsecond replenishing means becomes a predetermined number; judging meansfor judging whether the first and second developers have same color;selecting means responsive to said detecting means, counting means andjudging means for automatically selecting said second developing meansin the case where the continuous number of replenishment to the firstdeveloper by said second replenishing means becomes the predeterminednumber and where the toner density in the second developer is not lessthan the specified value under the judgment by said judging means thatthe first and second developers have same color; and means responsive tosaid detecting means, counting means and judging means or prohibiting animage forming operation during replenishment to the first developer bysaid third replenishing means in the case where the continuous number ofreplenishment to the first developer by said second replenishing meansbecomes the predetermined number and where the toner density in thesecond developer is not less than the specified value even if the firstand second developers have same color.

By the arrangement according to the present invention, in the case wheredocuments having images with much solid portion are continuously copied,even if density of toner accommodated into the developing means in usingis lower than the determined reference level, the device to be used ischanged over from the developing means in using to the other developingmeans, so that the images are continuously developed by the otherdeveloping means having toner with the same color as that of the tonerin the developing means using. Therefore, in the apparatus, a waitingtime period is less than before and many documents can be copied in ashort time while keeping images of copied papers in good quality.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome apparent from the following description taken in conjunction withthe preferred embodiment thereof with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic sectional view of a copying apparatus according tothe present invention;

FIG. 2 is a top plan view of an original platform of the copyingapparatus;

FIG. 3 is a top plan view of an operating panel of the copyingapparatus;

FIGS. 4 and 5 are sectional views of a developing device of the copyingapparatus;

FIG. 6 is a perspective view of a toner replenishment mechanism of thecopying apparatus;

FIG. 7 is a perspective view of a bristle regulating mechanism of thecopying apparatus of FIG. 1;

FIG. 8 is a circuit diagram of control of the copying apparatus of FIG.1;

FIG. 9 is an explanatory view of time setting of a timer in the copyingapparatus of FIG. 1;

FIGS. 10, 11 and 12 are timing charts indicative of operation of abristle regulating shutter, etc. at the time of simultaneous colorcopying, color copying and black copying in the copying apparatus ofFIG. 1, respectively;

FIGS. 13 and 14 are timing charts indicative of control of replenishmentat the time of simultaneous color copying, color copying and blackcopying;

FIG. 15 is a flow chart of a main routine of processing sequences ofoperation of the copying apparatus of FIG. 1;

FIG. 16 is a flow chart of a subroutine for bristle regulation in thecopying apparatus of FIG. 1;

FIGS. 17 to 27 are flow charts showing bristle regulating states in thecopying apparatus of FIG. 1;

FIG. 28 is a flow chart of a subroutine for automatic two-colorchangeover in the copying apparatus of FIG. 1;

FIGS. 29 to 32 are flow charts showing two-color states in the copyingapparatus of FIG. 1;

FIG. 33 is a flow chart of a subroutine for automatic toner densitycontrol (ATDC) in the copying apparatus of FIG. 1;

FIGS. 34 to 42 are flow charts showing ATDC states in the copyingapparatus of FIG. 1;

FIG. 42A is a flow chart of a subroutine for special black tonerreplenishment in the copying apparatus of FIG. 1;

FIG. 42B is a flow chart of a subroutine for special color tonerreplenishment in the copying apparatus of FIG. 1;

FIG. 43 is a flow chart of a subroutine for detecting by ATDC sensors inthe copying apparatus of FIG. 1;

FIG. 44 is a flow chart of a subroutine for paper feed control in thecopying apparatus of FIG. 1;

FIGS. 45 to 47 are flow charts showing paper states in the copyingapparatus of FIG. 1;

FIG. 48 is a flow chart of a subroutine for control elements providedaround a photosensitive drum in the copying apparatus of FIG. 1;

FIGS. 49 to 53 are flow charts showing drum states in the copyingapparatus of FIG. 1;

FIG. 54 is a flow chart of a subroutine for automatic reset in thecopying apparatus of FIG. 1; and

FIG. 55 is a flow chart of a subroutine for automatic changeover ofdeveloping devices in the copying apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Before the description of the present invention proceeds, it is to benoted that like parts are designated by like reference numerals andsymbols throughout the accompanying drawings.

I. General construction and operation

Referring now to the drawings, there is shown in FIG. 1, an imageforming apparatus in the form of a movable original platform typetwo-color copying apparatus 1 to which the present invention may beapplied. Hereinbelow, general construction and copying operation of thecopying apparatus 1 are described.

Initially, in a state where a photosensitive or photoreceptor drum 2 isrotated in the direction of the arrow by a main motor (not shown), atransfer charger 7, an exposure lamp 11 of an optical system 0, etc. areturned on and the surface of the photosensitive drum 2 is electricallycharged by a corona charger 3 on a precondition that electric charge ofan image nonforming portion of the photosensitive drum 2 is erased by aneraser 4. It is to be noted that the image nonforming portion of thephotosensitive drum 2 corresponding to an area of a glass plate 21,which is disposed forwardly of a front edge of an original document (notshown) placed on the glass plate 21 and rearwardly of a rear edge of theoriginal document in a scanning direction of the original document,respectively.

When the photosensitive drum 2 and its peripheral devices have been setas described above, reflected light of light emitted from the exposurelamp 11 to the surface of the original document is projected onto thesurface of the photosensitive drum 2 through mirrors 12, 13, 14 and 15and a lens 16 while an original platform 20 is being displaced in therightward direction of the arrow by a scanning motor (not shown). Thus,an electrostatic latent image corresponding to an image of the originaldocument is formed on the surface of the photosensitive drum 2.

In response to rotation of the photosensitive drum 2, this electrostaticlatent image is passed through areas confronting first and seconddeveloping devices 5 and 6. At this time, toners are supplied to theelectrostatic latent image from the first and second developing devices5 and 6 such that the electrostatic latent image is formed into avisible toner image.

Meanwhile, when the copying apparatus 1 is set to a black copying modeor a color copying mode, black toner or color toner is, respectively,supplied to the electrostatic latent image from the second developingdevice (black developing device) 6 or the first developing device (colordeveloping device) 5. Meanwhile, when the copying apparatus 1 is set toa simultaneous color copying mode in which a two-color copy is obtainedthrough changeover from the first developing device 5 to the seconddeveloping device 6 during one scanning operation, the color toner issupplied from the first developing device 5 to one portion of theelectrostatic latent image, which corresponds to one portion of theoriginal document extending from its front edge of scanning to apredetermined changeover point. Meanwhile, the black toner is suppliedfrom the second developing device 6 to the other portion of theelectrostatic latent image, which corresponding to the other portion ofthe original document extending from the changeover point to its rearedge.

A copy paper sheet is fed from a paper feeding mechanism 30 and is heldin a waiting state at a location disposed upstream of timing rollers 35in a paper feeding direction. The copy paper sheet in a waiting state istransported, synchronously with the image on the photosensitive drum 2,to an area where the photosensitive drum 2 and a transfer charger 7confront each other. At this area, the toner image is transferred ontothe copy paper sheet by the transfer charger 7.

The copy paper sheet having the toner image transferred thereon isseparated from the surface of the photosensitive drum 2 by a separatingbelt 8 and is further conveyed by transport rollers 43 to a fixingdevice 41 where the toner image of the copy paper sheet is fixed,through fusion thereof, on the copy sheet. Finally, the copy paper sheethaving the fixed toner image is ejected to a paper discharge portion 42.

Meanwhile, residual toner on the surface of the photosensitive drum 2 isremoved by a cleaning device 9 so as to be collected into the cleaningdevice 9. Meanwhile, residual electric charge on the surface of thephotosensitive drum 2 is erased by a main eraser 10 which is held in theON state during drive of the main motor.

II. Various devices

Hereinbelow, the various devices constituting the copying apparatus aredescribed in more detail.

(1) Optical system (0)

The optical system 0 is constituted by the exposure lamp 11 of slitexposure type, the mirrors 12 to 15 and the lens 16 which are secured inposition as shown. Reflected light of light emitted from the exposurelamp 11 to the original platform 20 proceeds in a path shown by theone-dot chain lines so as to be projected, between the corona charger 3and the eraser 4, onto the surface of the photosensitive drum 2.

(2) Original platform (20)

The original platform 20 is constituted by the glass plate 21 and anoriginal holding plate 22 which can be opened or closed relative to thesurface of the glass plate 21. The original platform 20 is displaced,for scanning, in the direction of the arrow at a speed V. Assuming thatcharacters Vo and m denote a peripheral speed of the photosensitive drum2 and a copying magnification, respectively, the following relation isestablished.V=Vo/m

As shown in FIG. 2, a starting-point mark A and point marks 1P to 0P areprovided at intervals of 30 mm at one side of the glass plate 21, whichis disposed at an operator's side. These marks A and 1P to 0P are usedfor designating the changeover point of the developing colors in thesimultaneous color copying mode. Meanwhile, character B denotes areference point for positioning an original document G at the time ofactual copying of the original document G.

A positioning switch 23 and a register switch 24 are provided below theoriginal platform 20. When scanning is not being performed, i.e. thecopying apparatus 1 is at a stop, the original platform 20 is broughtinto contact with the positioning switch 23 so as to output apositioning signal to a first CPU (central processing unit) 200 to bedescribed later. At the time when the glass 21 has been displaced, forscanning, through a predetermined distance, the original platform 20 isbrought into contact with the register switch 24 so as to output to thefirst CPU 200 a register signal not only for actuating the timingrollers 35 but for effecting changeover between the first and seconddeveloping devices 5 and 6 at the time of simultaneous color copying.

Meanwhile, setting of the changeover point of the developing colors isperformed as follows. As shown in FIG. 2, the original document G isplaced on the glass plate 21 by orienting the front face of the originaldocument G upwardly such that the right end of the original document Gcoincides with the starting-point mark A. Then, a desired changeoverpoint Po of the developing colors is set.

For example, in the case where regions R1 and R2 of the originaldocument G, which occupy right and left portions of the originaldocument G separated from each other by the broken line, are developedin the color and black, the point mark 4P coinciding with the brokenline is set as the changeover point Po by operating a color selectionswitch 121 and then keys 106 to 115 in a method to be described indetail later.

Subsequently, the original document G is turned over such that the frontface of the original document G, which has an image thereon, is orienteddownwardly and the left end of the original document G coincides with areference point B as shown by the left one-dot chain line.

(3) Paper feeding mechanism (30)

The paper feeding mechanism 30 includes a manual paper feeding portion31, a first paper feeding portion 32 having a cassette 32a and a secondpaper feeding portion 33 having a cassette 33a. A copy paper sheetinserted from the manual paper feeding portion 31 is transported, viaintermediate rollers 34, to the timing rollers 35. Meanwhile, copy papersheets in the cassette 32a loaded into the first paper feeding portion32 are conveyed to the timing rollers 35 through a first paper feedingroller 32b and the intermediate rollers 34, while copy paper sheets inthe cassette 33a loaded into the second paper feeding portion 33 arecarried to the timing rollers 35 by way of a second paper feeding roller33b.

The above described rollers 32b, 33b, 34 and 35 are detachably coupledwith a drive unit of the main motor through clutches (not shown),respectively. By turning on the clutches of the respective rollers, therollers are coupled with the drive unit so as to be driven for rotationthereof by the main motor. In the vicinity of the cassette 32a, thereare provided a size sensor 36a for detecting size of the copy papersheets contained in the cassette 32a and a cassette empty sensor 38 fordetecting a state that all the copy paper sheets in the cassette 32ahave been consumed. Likewise, in the vicinity of the cassette 33a, asize sensor 37a and a cassette empty sensor 39 are provided.

(4) Operating panel

At an upper portion of the copying apparatus 1, an operating panel 100shown in FIG. 3 is provided. The operating pane 100 includes a printswitch 102 for commanding start of copying, an automatic reset key 103and a clear/stop key 105 not only for suspending copying immediatelyafter start of copying or in the course of multi-copying for continuouscopying an identical original document into a plurality of copies butfor reinstating to a standard mode "1" the number of copies set at acopy quantity display portion 104 composed of groups of LEDs by clearingthe number of copies set at the cop quantity display portion 104. Theoperating panel 100 further includes the ten keys 106 to 115 for settingthe number of copies in the copy quantity display portion 104, anexposure volume VR for manually increasing or decreasing exposure amountfrom the exposure lamp 11, a selection switch 117 for selecting anautomatic exposure mode in which an optimum exposure amount isautomatically set for an original document, a selection key (not shown)for selecting one of the first and second paper feeding portions 32 and33, an LED (not shown) for displaying size of the copy paper sheets fedfrom the selected one of the first and second paper feeding portions 32and 33, a color selection key 121 for selecting one of the first andsecond developing devices 5 and 6 and LEDs 127 and 126 for displayingthe selected one of the first and second developing devices 5 and 6,respectively.

Furthermore, the operating panel 100 includes an LED 132 for displayinga state that the selected one of toner replenishment bottles 81 and 91mounted on the first and second developing devices 5 and 6 is empty, aselection key 122 for selecting a book division mode and an LED 128 fordisplaying a state that the book division mode is selected. Although notspecifically shown, the operating panel 100 includes a switch forstarting drying of the photosensitive drum 2 and a switch for startingforcible replenishment of the toner.

(5) Developing device

The developing devices 5 and 6 are of a type employing two-componentdeveloper composed of toner and carrier. Initially, the seconddeveloping device 6 disposed at the downstream side in the rotationaldirection of the photosensitive drum 2 is described with reference toFIGS. 4 and 5, hereinbelow. It is to be noted that numerals inparentheses in FIGS. 4 and 5 represent components of the firstdeveloping device 5.

(a) Construction of the second developing device (6)

In the second developing device 6, a developing sleeve 61 is rotatablyprovided at a front portion of a casing 60 so as to confront thephotosensitive drum 2. A developing bias voltage of -150V is applied tothe developing sleeve 61. A magnetic roller 62 is fixedly provided inthe developing sleeve 61. In the magnetic roller 62, a plurality ofmagnets having axially extending magnetic poles S and N are arranged asshown. At an outer peripheral portion of the magnetic roller 62 oppositeto the photosensitive drum 2, two S-poles are provided adjacent to eachother so as to form a magnetized portion Z having two neighboringmagnetic poles of an identical polarity.

At a rear portion of the developing sleeve 61, transport passages 63 and64 are formed and a bucket roller 65 and a transport roller 66 arerotatably provided at the transport passages 63 and 64, respectively.The transport passages 63 and 64 are partially separated from each otherby a partition wall 67 upwardly extending from the casing 60. However,although not specifically shown, the transport passages 63 and 64 arecommunicated with each other through openings formed at far and nearsides of the partition wall 67 as observed in a direction perpendicularto the sheet of FIGS. 4 and 5.

Meanwhile, at a bottom portion of the rear transport passage 64, a tonerdensity sensor AS2 for detecting, as change of permeability, density ofthe toner in the two-component developer composed of the toner and thecarrier (referred to as an "ATDC (automatic toner density control)sensor", hereinbelow) is provided such that its detection face isbrought into contact with the developer in the transport passage 64. Anoutput signal of the ATDC sensor AS2 is applied to the first CPU 200 ofa control circuit to be described later.

Meanwhile, in the copying apparatus 1 in which a plurality of thedeveloping devices 5 and 6 are provided around the photosensitive drum2, the following problems may arise. Namely, if the developer of thesecond developing device 6 is held in contact with the photosensitivedrum 2 in the case where development is performed by using the firstdeveloping device 5, the toner image formed on the surface of thephotosensitive drum 2 by the first developing device 5 is disturbed bythe developer of the second developing device 6. Meanwhile, if thedeveloper of the first developing device 5 is held in contact with thephotosensitive drum 2 in the case where development is performed byusing the second developing device 6, the electrostatic latent image onthe photosensitive drum 2 is initially developed by the first developingdevice 5, thereby resulting in mixing of colors.

Therefore, as a first countermeasure for preventing such mixing ofcolors, a bristle shutter 71 is provided between the developing sleeve61 and the bucket roller 65 in the second developing device 6. Whendevelopment is performed by using the first developing device 5, thedeveloper held on the surface of the developing sleeve (seconddeveloping device) 61 is removed therefrom by using the bristle shutter71. The bristle shutter 71 can be changed over the states of FIGS. 4 and5 by a changeover means 70 shown in FIG. 7.

(b) Changeover means (70)

As shown in FIG. 7, the bristle shutter 71 is rotatably attached to thecasing 60 through a pair of support shafts 72 and 72 secured to oppositeends of the bristle shutter 71. A lever 73 is secured to one of thesupport shafts 72 and 72. A spring 74 having one end attached to thecasing 60 is fitted to a distal end portion of the lever 73 so as tourge the lever 73 in the direction of the arrow a. Meanwhile, a plunger76 of a solenoid is rotatably coupled with the lever 73 such that thelever 73 is held in a stable state. Reference numeral 77 denotes astopper.

Therefore, when the solenoid 75 is in the OFF state, the bristle shutter71 is urged by the spring 74 into the OFF state of FIG. 4. On the otherhand, when the solenoid 75 is turned on, the lever 73 is rotated in thedirection of the arrow a' against the urging force of the spring 74 soas to be brought into contact with the stopper 77, so that the bristleshutter 71 is set to the ON state of FIG. 5.

(c) First developing device (5)

The first developing device 5 is substantially identical, inconstruction, with the second developing device 6 and numerals inparentheses in FIGS. 4 and 5 represent components of the seconddeveloping device 6. Namely, as in the second developing device 6,transport passages 53 and 54 separated from each other by a partitionwall 57 are formed in a casing 50. Furthermore, a developing sleeve 51,a magnetic roller 52, a bucket roller 55 and a transport roller 56 areaccommodated in the casing 50 as shown. In addition, an ATDC sensor ASlis secured in the transport passage 54.

However, the first developing device 5 is different from the seconddeveloping device 6 in that in the first developing device 5, thebristle shutter 71 is not provided and a developing bias voltage (firstdeveloping bias voltage) (not shown), serving as a second countermeasurefor preventing the mixing of colors, applied to the first developingsleeve 51 can be changed over to two stages of -150V and -300V. Hence,the first developing device 5 is not provided with the changeover means70 for the bristle shutter 71.

Meanwhile, the first and second developing devices 5 and 6 are coupled,for drive thereof, with the main motor (not shown) such that the drivingforce of the main motor is selectively transmitted to only one of thedeveloping devices 5 and 6 by a sleeve solenoid (not shown).

Namely, when the main motor is coupled, for drive thereof, with thefirst developing sleeve 51, the driving force of the main motor is nottransmitted to the second developing sleeve 61. On the contrary, whenthe main motor is coupled, for drive thereof, with the second developingsleeve 61, the driving force of the main motor is not transmitted to thefirst developing sleeve 51.

Furthermore, although it is constructed such that the developing devices5 and 6 are selectively changed over by the sleeve solenoid as describedabove, a drive means such as motor can be provided in the first andsecond developing devices 5 and 6, respectively, so that each device isindependently driven.

(d) Toner replenishment mechanism and toner color detection mechanism

FIG. 6 shows a toner replenishment mechanism for replenishing the firstdeveloping device 5 with toner. Since a toner replenishment mechanismfor replenishing the second developing device 6 with toner is identical,in construction, with the toner replenishment mechanism for replenishingthe first developing device 5 with toner, numerals in parenthesesrepresent the toner replenishing mechanism for the second developingdevice 6.

A bracket 80 is mounted on one end of the developing device 5. The tonerreplenishment bottle 81 for replenishing toner to the rear transportpassage 54 in the developing device 5 is detachably mounted on thebracket 80 so as to replenish the toner while being rotated by areplenishment motor (not shown).

In the vicinity of the toner replenishment bottle 81, a sensor 82 fordetecting presence and absence of the toner replenishment bottle 81 isprovided such that presence and absence of the bottle 81 are judged byON and OFF signals of the sensor 82. A toner empty sensor 83 fordetecting presence and absence of the toner in the bottle 81 is providedat a mouth of the bottle 81. Magnets 84 and 85 for detecting color oftoner contained in the casing 50 are attached, side by side, to an upperportion of the developing device 5.

Meanwhile, first and second reed switches 86 and 87 are provided at thecopying apparatus so as to confront the magnets 84 and 85, respectively,in a state where the first developing device 5 is mounted on the copyingapparatus. As shown in Table 1 below, the color of the toner containedin the first developing device 5 is judged by combination of ON and OFFsignals of the first and second reed switches 86 and 87.

                  TABLE 1                                                         ______________________________________                                        First switch (86)                                                                          Second switch (87)                                                                              Toner                                          ______________________________________                                        ON           ON                Black                                          ON           OFF               Red                                            OFF          ON                Yellow                                         OFF          OFF               Blue                                           ______________________________________                                    

If the first developing device 5 contains red toner, only the magnet 84corresponding to the first reed switch 86 is attached to the firstdeveloping device 5 and the magnet 85 corresponding to the reed switch87 is not attached to the first developing device 5 so that only thefirst reed switch 86 is turned on.

(e) Developing operation

In the developing devices 5 and 6 of the above described arrangement,the two-component developer composed of the toner and the carrier iscontained in the casings 50 and 60, respectively. Namely, the colortoner and the black toner are, respectively, contained in the first andsecond developing devices 5 and 6. The developer is transported, for itscirculation, through the transport passages 54 and 53 upon rotation ofthe transport roller 56 and the bucket roller 55 in the first developingdevice 5 and through the transport passages 64 and 63 upon rotation ofthe transport roller 66 and the bucket roller 65 in the seconddeveloping device 6. At this time, the toner and the carrier are mixedwith each other into the two-component developer of uniformconcentration and the toner is electrically charged through frictionalcontact between the toner and the carrier.

Meanwhile, in the course of transport of the developer, a portion of thedeveloper is supplied to the surface of the developing sleeve 51 or 61and is held in a state of the magnetic brush along lines of magneticforce generated from the magnetic roller 52 or 62.

The developer held on the surface of the developing sleeve 51 or 61 istransported in a state of a magnetic brush in the direction of the arrowthrough rotation of the developing sleeve 51 or 61 and the magneticbrush is brought into sliding contact with the surface of thephotosensitive drum 2 at an area confronting the photosensitive drum 2.Thus, on the basis of difference between surface potential of thephotosensitive drum 2 and the developing bias voltage applied to thedeveloping device 5 or 6, the magnetic brush is transferred to theelectrostatic latent image formed on the surface of the photosensitivedrum 2 so as to develop the electrostatic latent image into the visibletoner image.

The developer having passed through the area confronting thephotosensitive drum 2 is successively conveyed in the direction of thearrow through rotation of the developing sleeve 51 or 61. When thedeveloper on the developing sleeve 51 or 61 reaches an area confrontingthe bucket roller 55 or 65, the developer is separated from the surfaceof the developing sleeve 51 or 61 by action of a repulsive magneticfield formed by the magnetized portion Z having two neighboring magneticpoles of an identical polarity and is mixed into the developer into thetransport passage 53 or 63.

Meanwhile, the bristle shutter 71 is provided in the second developingdevice 6. Thus, if the developing device 6 is driven when the bristleshutter 71 is in the OFF state of FIG. 4, the developer discharged fromthe bucket roller 65 towards the developing sleeve 61 is guided by thebristle shutter 71 so as to proceed in the direction of the arrow X suchthat the developer is supplied to the surface of the developing sleeve61. On the other hand, the developer separated from the developingsleeve 61 is carried below the bristle shutter 71 so as to be collectedfrom the direction of the arrow Y into the transport passage 63.

However, even if the developing device 5 is driven in the ON state ofthe bristle shutter 71 shown in FIG. 5, the developer discharged fromthe bucket roller 65 towards the developing sleeve 61 is blocked by thebristle shutter 71 so as to return in the direction of the arrow X', sothat the developer is not supplied to the surface of the developersleeve 61. Meanwhile, the developer held on the surface of thedeveloping sleeve 61 is collected into the transport passage 63 in thesame way as the above-described and thus, substantially no developer ispresent on the developing sleeve 61. Therefore, when development isperformed in this state by using the first developing device 5, such aphenomenon does not take place that the toner image formed by the firstdeveloping device 5 is disturbed by the developer of the seconddeveloping device 6.

By repetition of the above described developing operation in thedeveloping devices 5 and 6, the toners in the developing devices 5 and 6are gradually consumed, thereby resulting in drop of density of thetoners.

When it is detected from a signal outputted from the ATDC sensor AS1 orAS2 to a microcomputer to be described later that the above describedtoner density has dropped lower than a predetermined control level, thetoner is replenished from the toner replenishment bottle 81 or 91 to thetransport passage 54 or 64 in response to a signal from themicrocomputer. This newly replenished toner is conveyed through thetransport passages 54 and 53 by the transport roller 56 and the bucketroller 55 in the first developing device 5 and through the transportpassages 64 and 63 by the transport roller 66 and the bucket roller 65in the second developing device 6 so as to be mixed with the carriersuch that the two-component developer is adjusted.

(6) Circuit configuration

The copying apparatus 1 incorporates the microcomputer (not shown) andthe microcomputer has such a circuit configuration as shown in FIG. 8.In FIG. 8, the microcomputer includes the first CPU 200 and a second CPU300. A key matrix S including the various keys on the operating panel100, the first and second toner empty sensors 83 and 93, the first andsecond bottle empty sensors 82 and 92, the reed switches 84, 85, 94 and95, etc. arranged in a pattern of a matrix, the ATDC sensors AS1 andAS2, the positioning switch 23 and the register switch 24 are connectedto the first CPU 200. The main motor, the various roller clutches, etc.are operated and controlled by the first CPU 200 upon operation of thevarious keys and actuation of the various sensors and the various LEDsincluding the copy quantity display portion 104 having display portions104a and 104b are turned on and off by the first CPU 200 through adecoder 133.

On the other hand, the positioning switch 23, the register switch 24,etc. are connected to the second CPU 300. The second CPU 300 is mainlyused or operating and controlling the optical system 0. In order tosynchronize the first and second CPUs 200 and 300 with each other, thefirst and second CPUs 200 and 300 are connected to each other. III.Control

Hereinbelow, control procedures of the copying apparatus 1 are describedwith reference to the accompanying flow charts.

(1) Main routine (FIG. 15)

In a main routine of the control procedures of the copying apparatus 1,when operation of the microcomputer is started by turning on a powersource of the copying apparatus 1, initial values of various parametersare set at step M1. At step M2, an internal timer is started. Thisinternal timer is reset at the preceding step M1 and is used fordetermining a time period for executing one routine of the main routine.Various timers to be described in the following subroutines decide lapseof their preset time periods by the numbers of counts in one routine ofthe internal timer.

Then, each of subroutines of steps M3 to M18 is sequentially called.When proceeding of all the subroutines has been completed, lapse of thepreset time period of the internal timer is waited for at step M19 andthen, the program flow returns to step S2. Meanwhile, the steps M3 to M6are subroutines for processing signals inputted from the various keys ofthe operating panel 100. Namely, the step M3 is a subroutine forprocessing input and output signals, the step M4 is a subroutine forprocessing a signal from the color selection key 121, the step M5 is asubroutine for processing a signal inputted from the ten keys 106 to 115and the step M6 is a subroutine for processing signals of otherswitches.

Steps M7 to M9 are a process for controlling display of the operatingpanel 100. Namely, the step M7 is a subroutine for displaying, at thedisplay portion 104 of the operating panel 100, the changeover point Poin the simultaneously color copying mode or the number of copies. Thestep M8 is a subroutine for displaying the developing device to be usedin accordance with the copying modes. The step M9 is a subroutine fordisplaying a toner empty state.

Steps M10 to M13 are subroutines for controlling operation of thedeveloping devices 5 and 6. Namely, the step M10 is a subroutine forprocessing the bristle shutter 71. The step M11 is a subroutine foreffecting changeover of drive of the developing devices 5 and 6 in thesimultaneous color copying mode. The steps M12 and M13 are subroutinesfor controlling density of the toners in the developing devices 5 and 6.

Step M14 is a subroutine for controlling transport of copy paper sheetsof the paper feeding mechanism 30, etc. Step M15 is a subroutine forcontrolling the photosensitive drum 2 and its peripheral devices. StepM16 is a subroutine for initializing copying mode of the copyingapparatus. Step M17 is a subroutine for effecting changeover of use ofother developing device in the state where though usual tonerreplenishment is performed, the value of toner density is not over thepredetermined value. Step M18 is a subroutine for processing othercontrols.

Hereinbelow, the subroutines for controlling operation the copyingapparatus according to the present invention are described.

(2) Subroutines

Hereinbelow, the subroutines for controlling operation of the copyingapparatus 1 are described. Meanwhile, the relation between copying modeflags FCOLOR and F2COLOR and black, color and simultaneous color copyingmode used in the following subroutines is set as shown in Table 2 below.At the time the power source of the copying apparatus 1 has been turnedon, the copying mode flags FCOLOR and F2COLOR are set to 0 at theinitialization subroutine (step M1) of the main routine so as to set tothe black copying mode.

                  TABLE 2                                                         ______________________________________                                        Copying mode     FCOLOR    F2COLOR                                            ______________________________________                                        Black            0         0                                                  Color            1         0                                                  Simultaneous color                                                                             1         1                                                  ______________________________________                                    

(A) Bristle regulating subroutine (step M10)

For this bristle regulating subroutine, reference should be made to flowcharts of FIGS. 16 to 27 and timing charts of FIGS. 10 to 12. In thisbristle regulating subroutine, changeover among the bristle shutter 71of the second developing device 6, the drive units of the first andsecond developing devices 5 and 6 and the first developing bias voltageis performed in accordance with conditions at each point of time.

In the bristle regulating subroutine, a bristle regulation state No. HSNis judged in accordance with the flow chart of FIG. 16. On the basis ofvalues of the bristle regulation state No. HSN, the program flowproceeds to steps SH0 to SHA for predetermined bristle regulation states0 to A, respectively. Meanwhile, when the power source of the copyingapparatus 1 has been turned on, the bristle regulation state No. HSN isset to 0 at the initialization subroutine M1 of the main routine andthus, the program starts from the bristle regulation state 0.

Bristle regulation state 0 (FIG. 17)

In the bristle regulation state 0, it is found at step SH000 that a flagFCPRQU, which is set by through turning-on of the print switch 102,indicating that there is a demand for copying is 1. If it is detectedthat the flag FCPRQU is 1, the main motor has been turned on. Then, atstep SH001, a decision is made as to whether either the simultaneouscolor copying mode or the color copying mode is selected or the blackcopying mode is selected. If either the simultaneous color copying modeor the color copying mode is selected, the program flow proceeds tosteps SH002 to SH004. If the black copying mode is selected, the programflow proceeds to step SH010.

Then, in the case of the simultaneous color copying mode r the colorcopying mode, a decision is made at step SH002 as to whether or not a2-color state No. 2SN set in an automatic 2-color changeover subroutineto be described later is set to 0. In the case of "YES" at step SH002, atimer Tsh-A for delaying turning on of the bristle shutter 71 is set atstep SH003 and the bristle regulation state No. HSN is set to 1 at stepSH004 and then, the program flow returns. Reference should be made to atime chart of the simultaneous color copying mode of FIG. 10 and a timechart of the color copy mode of FIG. 11. This timer Tsh-A is used forstarting bristle regulation after the developing sleeve 61 of the seconddeveloping device 6 has been fully rotated.

When the copying apparatus 1 is in a waiting state (FCPRQU=0) or theblack copying mode (FCOLOR=0) is selected, the program flow proceeds tostep SH010 at which a decision is made as to whether or not a flag FCOPYindicating that copying is being performed is set to 1.

Subsequently, in the case of the "NO" (FCOPY=0) at step SH010, adecision is made at step SH020 as to whether or not a tonerreplenishment mode is selected and then, a decision is made at stepSH021 as to whether or not a drum dry mode for drying the photosensitivedrum 2 is selected. Furthermore, the copying mode is judged at stepsSH011 and SH030. In accordance with the selected copying modes, thedrive units of the developing devices and the developing bias voltagesare set to predetermined states in the subsequent steps SH012 to SH014,SH022, SH023, SH031 and SH033.

Namely, if the black copying mode is selected, at steps SH022 and SH023,the main motor is coupled with the second developing device 6 for drivethereof so as to be set to a black mode, while the first and seconddeveloping bias voltages are set to a black level, i.e. -300V and -150V,respectively. Reference should be made to a time chart of the blackcopying mode of FIG. 12.

On the other hand, if the color copying mode or the simultaneous colorcopying mode is selected, the main motor is coupled with the firstdeveloping device 5 for drive thereof so as to be set to a color mode,while the first and second developing bias voltages are set to a colorlevel, i.e. -150V. If the toner replenishment mode is selected at stepsSH020 and SH021 and the drum dry mode is selected, in spite of thecopying mode, the units of the developing device is set to the blackcopying mode and the developing bias voltage is set to the black level.

Subsequently, at step SH014, the bristle shutter 71 is turned off andthen, at step SH015, a decision is made as to whether or not there is ademand for copying. If it is found at step SH015 that the flag FCPRQU is1, the bristle regulation state No. HSN is set to 4 so as to execute theblack copy at step SH016 and then, the program flow returns such thatchangeover of rotation of the developing sleeves, the developing biasvoltages and the bristle shutter 71 is prohibited during the subsequentcopying. Meanwhile, if the flag FCPRQE is 0, the program flow returns soas to be in a waiting state.

Bristle regulation state 1 (FIG. 18)

In the bristle regulation state 1, a decision is made at step SH100 asto whether or not the timer Tsh-A set at the above described step SH003has timed. In the case of "YES" at step SH100, the bristle shutter 71 isset to the ON state of FIG. 5 at step SH101, a timer Tsh-B for removingthe black toner is. set at step SH102 and the bristle regulation stateNo. HSN is set to 2 at step SH103 and then, the program flow returns.Meanwhile, the timer Tsh-B is used for removing the developer from thesurface of the second developing sleeve 61 by the bristle shutter 71prior to start of color developing, so that the color toner image formedby the first developing device 5 is not disturbed at an area confrontingthe second developing device 6. On the other hand, if the timer Tsh-A iscounting a preset time period, a decision is made at step SH110 as towhether or not copying is being performed. If copying is beingperformed, copying operation is continued. If copying is not performedsince copying is interrupted by the clear/stop key 105, etc., thebristle regulation state No. HSN is set to 0 at step SH111 and theprogram flow returns.

Bristle regulation state 2 (FIG. 19)

In the bristle regulation state 2, a decision is made at step SH200 asto whether or not the timer Tsh-B has timed. If the timer Tsh-B iscounting a preset time period, the program flow proceeds to step SH110and SHlll so as to remain in a waiting state. On the other hand, whenthe developer on the second (black) developing sleeve 61 has beenremoved after completion of counting of the timer Tsh-B, steps SH201 toSH204 are executed and the program flow returns.

Meanwhile, at step SH201, rotation of the developing sleeve is changedover to the color copying mode such that the developing sleeve 51 of thefirst developing device 5 is started, while the second developing device6 is stopped. At step SH202, the first developing bias voltage ischanged from the black level of -300V to the color level of -150V. Atstep SH203, a timer Tsh-C for delaying turning off of the bristleshutter 71 is set and the bristle regulation state No. HSN is set to 3at step SH204 such that the copying apparatus 1 is set to a stateenabling color copying.

Bristle regulation state 3 (FIG. 20)

In the bristle regulation state 3, if the timer Tsh-C is counting apresent time period, the program flow proceeds to step SH110 and SH111so as to remain in a waiting state at step SH300. If the timer Tsh-C hastimed at step SH300, a decision is made at step SH301 as to whether ornot the simultaneous color copying mode is selected. In the case of"YES" at step SH301, the program flow skips step SH302 for turning offthe bristle shutter 71 so as to proceed to step SH303 at which thebristle regulation state No. HSN is set to 4.

Namely, if it is found at step SH301 that the simultaneous color copyingmode is selected, the bristle shutter 71 is set in the ON state of FIG.5 until black development is started by the second developing device 6.

In the case of the color copying mode, the program flow proceeds fromstep SH301 to step SH302 at which the bristle shutter 71 is turned off,as shown in a time chart of FIG. 11. Then, at step SH303, the bristleregulation state No. HSN is set to 4 at step SH303 and the program flowproceeds to the bristle regulation state 4. This program schema isemployed on the following ground. Namely, in the color copying mode,etc., if the developer has been removed from the surface of the seconddeveloping sleeve 61 by turning on the bristle shutter 71, the blackdeveloper is not supplied onto the second developing sleeve 61subsequently, so that color copying can be continued without anyproblem. Then, upon lapse of a preset time period of a timer Tsc-C to bedescribed later, the bristle shutter 71 is changed over to the OFFstate.

Bristle regulation state 4 (FIG. 21)

In the bristle regulation state 4, a timer Tsh-D for delaying permissionof mode change is set at step SH400. Then, at step SH401, a decision ismade as to whether or not copying is being performed. In the case of"NO" at step SH401, a decision is made at step SH420 as to whether ornot the flag F2COLOR is 1 and then, a decision is made at step SH421 asto whether or not scanning has been completed. If not only thesimultaneous color copying mode is selected but scanning is beingperformed, the bristle regulation state No. HSN is set to A at stepSH422 and then, the program flow returns.

Meanwhile, in the case of "NO" at least either one of steps SH420 andSH421, the program flow returns. In the case of the simultaneous colorcopying mode, bristle regulation and changeover of the sleeve solenoidand the developing bias voltage in the waiting state are controlled inan automatic 2-color control subroutine to be described later. In thecase of the color copying mode, the bristle regulation state 4 ismaintained until completion of copying.

Meanwhile, in the waiting state, a timer Tsh-D is repeatedly set at stepSH400. However, since there is no step for judging whether or not thetimer Tsh-D has timed during execution of the bristle regulation state4, a series of operations are not controlled by the timer Tsh-D.

If it is found at step SH401 that the copy flag FCOPY is 0, namelycopying has been completed, the copying mode is judged at steps SH403and SH410. If the simultaneous color copying mode or the black copyingmode is selected, the bristle regulation state No. HSN is set to A atstep SH404 and the program flow returns. Meanwhile, if the color copyingmode is selected, the bristle regulation state No. HSN is set to 5 atstep SH411 and the program flow returns.

Meanwhile, if changeover of the developing bias voltage and rotation ofthe developing sleeve are performed immediately when changeover of thecopying mode has been performed, for example, the color copying mode hasbeen changed over to the black copying mode immediately after completionof copying, the black toner adheres to a trailing edge portion of thecolor copy. In order to prevent such a phenomenon, the timer Tsh-D isused for prohibiting change over of the copying mode until a point onthe photosensitive drum 2 has passed through at least an interval fromthe exposure position to an area confronting the developing device 6.

Bristle regulation state 5 (FIG. 22)

The bristle regulation state 5 is designed to perform processing aftercopying. At step SH500, a decision is made as to whether or not thetimer Tsh-D has timed. In the case of "YES" at step SH500, a decision ismade as to whether or not the flag FCOLOR is 1. In the case of "YES" atstep SH501, namely if the color copying mode or the simultaneous colorcopying mode is selected, the bristle regulation state No. HSN is set to6 at step SH502 such that bristle regulation is not performed again whenthe next copying is performed in the color copying mode.

On the other hand, if the flag FCOLOR is 0, namely the black copyingmode is selected, the bristle regulation state No. HSN is set to 0 atstep SH503 such that preparation for immediately starting black copyingis made.

Bristle regulation state 6 (FIG. 23)

In the bristle regulation state 6, a decision is made at step SH600 asto whether or not the main motor is in the OFF state. In the case of"YES" at step SH600, the bristle regulation state No. HSN is set to 7 atstep SH601. Meanwhile, if it is found at step SH610 that a drum dry modefor drying the photosensitive drum 2 or a toner replenishment mode isstarted prior to stop of the main motor, the bristle regulation stateNo. HSN is set to 0 at step SH611. In the case of "NO" at step SH610,the program flow proceeds to step SH620.

At step SH620, a decision is made as to whether or not the copy flagFCOPY is 1. If copying is restarted prior to stop of the main motor, thebristle regulation state No. HSN is set to 8 at step SH621. Namely, ifcopying is started successively after completion of copying, the programflow proceeds to the bristle regulation state 8.

Bristle regulation state 7 (FIG. 24)

In the bristle regulation state 7, a decision is made at step SH700 asto whether or not the developing bias voltage is in the OFF state. Inthe case of "NO" at step SH700, a decision is made at step SH710 as towhether or not the main motor is in the ON state. When the main motor isdriven for starting copying, drying of the photosensitive drum 2, foredreplenishment of the toner, etc., the bristle regulation state No. HSNis set to 8 at step SH711. In the case of "NO" at step SH710, theprogram flow returns.

Meanwhile, in the case of "YES" at step SH700, rotation of thedeveloping sleeve is set to the black mode at step SH701 and the bristleregulation state No. HSN is set to 8 at step SH702.

Namely, if the developing bias voltage is not turned off prior tocomplete stop of rotation of the main motor, the toner adheres from thedeveloping sleeve to the photosensitive drum 2 while the main motor isrotating by its inertia, thereby resulting in wasteful consumption ofthe toner. This bristle regulation state 7 is provided for preventingsuch waste of the toner.

Bristle regulation state 8 (FIG. 25)

In the bristle regulation state 8, a decision is made at step SH800 asto whether or not the print switch has been depressed again. In the caseof "YES" at step SH800, a decision is made at step SH801 as to whetheror not the color copying is selected. In the case of "YES" at stepSH801, steps SH802 to SH805 are successively executed. Namely, at stepSH802, rotation of the developing sleeve is set to the color copyingmode and drive is charged over to the first (color) developing device 5.Then, at step SH803, the first developing bias voltage is set to thecolor level of -150V and at step SH804, a timer Tsh-E is set. Then, atstep SH805, the bristle regulation state No. HSN is set to 9.

If changeover of the drive unit set hitherto to the black developingdevice 6 in the simultaneous color copying mode in view of powerconsumption, etc. and start of the main motor are performed at the sametime, the developing sleeve 61 of the black (second) developing device 6containing the black toner rotates slightly due to difference inresponse time therebetween, so that the black toner is supplied to thesurface of the photosensitive drum 2. In order to prevent such aphenomenon, the timer Tsh-E is used for driving the main motor after thedrive unit has been changed over to the color (first) developing device5.

On the other hand, if a signal from the print switch is not inputted,the program flow proceeds from step SH800 to step SH810 at which adecision is made as to whether or not the main motor is in the ON state.In the case of "YES" at step 810, the bristle regulation state No. HSNis set to 0 at step SH811. On the other hand, if the main motor is at astop, the program flow returns.

Meanwhile, if it is found at step SH801 that the copying mode other thanthe color copying mode is selected, the bristle regulation state No. HSNis set to 0 at step SH811 and the program flow returns.

Bristle regulation state 9 (FIG. 26)

In the bristle regulation state 9, a decision is made at step SH900 asto whether or not the timer Tsh-E has timed. In the case of "YES" atstep SH900, the bristle regulation state No. HSN is set to 4 at stepSH901 and the program flow returns.

Bristle regulation state A (FIG. 27)

In the bristle regulation state A, a decision is made at step SHA00 asto whether or not the timer Tsh-D has timed. In the case of "YES" atstep SHA00, the bristle regulation state No. HSN is set to 0 at stepSHA01 and the program flow returns. This timer Tsh-D is set in thebristle regulation state 4.

(B) Automatic 2-color changeover subroutine

Hereinbelow, the automatic 2-color changeover subroutines described withreference to FIGS. 28 to 32 and FIG. 10. This automatic 2-colorchangeover subroutine is directed to control of changeover of drivebetween the developing devices 5 and 6, changeover of the firstdeveloping bias voltage and changeover of the bristle shutter 71 inaccordance with the color changeover point Po in the simultaneous colorcopying mode. On the basis of the values of a 2-color state No. 2SNjudged at step SCA, the program flow proceeds to steps SC0 to SC3 for2-color state to 3, respectively. Meanwhile, at the time when thecopying apparatus 1 has been initialized, the 2-color state No. 2SN isset to 0.

2-color state 0 (FIG. 29)

In the 2-color state 0, a decision is made at steps SC00 to SC02 as towhether or not scanning of the simultaneously color copying mode isbeing performed. If the scanning is being performed, the program flowremains in a waiting state until it is found at step SC03 that theregister switch is in the ON state.

When the original platform 20 has turned on the register switch 24through depression thereof while being displaced for scanning, a timerTsc-A for delaying actuation of the sleeve solenoid is set at step SC04and the 2-color state No. 2SN is set to 1 at step SC05 and then, theprogram flow returns.

A preset time period of the timer Tsc-A changes according to a distancefrom the distal end of the original document to the color changeoverpoint Po and is automatically calculated and set by the microcomputerfrom data of the color changeover point Po inputted by manipulation ofthe keys of the operating panel 100. The preset time period of the timerTsc-A is set such that at the time when the timer Tsc-A has timed, apoint of the electrostatic latent image, which corresponds to thechangeover point Po of the regions R1 and R2 of the original document G,is just going to pass through an area confronting the first developingsleeve 51.

More specifically, it is assumed in the copying apparatus 1 thatCharacters L1 and L2 denote a distance from the transfer charger 7 tothe first developing sleeve 51 and a distance from the transfer charger7 to the timing rollers 35, respectively as shown in FIG. 9. Supposingthat the distance L1 is larger than the distance L2, a front edge Ps' ofthe electrostatic latent image, which corresponds to a front edge Ps ofthe image of the original document, is disposed at a position spacedabout a distance of (L1-L2) in the direction of the arrow from an areaconfronting the first developing sleeve 51 at the time when the registerswitch 23 has been turned on.

Therefore, on the supposition that character l denotes a distance fromthe front edge Ps of the original document at a scanning start side tothe color changeover point Po, a point Po' of the electrostatic latentimage, which corresponds to the color changeover point Po, is disposedat a point spaced a distance of [l-(L1-L2)] at an upstream side from thearea confronting the first developing sleeve 51. Thus, assuming thatcharacter Vo denotes a peripheral speed of the photosensitive drum 2,the preset time period TA of the timer Tsc-A is given by the followingequation. The time period TA denotes a period in which the colorchangeover point Po is just passing through the area confronting thefirst developing sleeve 51 from a point at that time when the registerswitch 23 has been turned on.

    TA=[l-(L1-L2)]/Vo

One concrete example is shown in table 3 below on such conditions asL1=81 mm, L2=55 mm and Vo=111 mm/sec.

                  TABLE 3                                                         ______________________________________                                        Changeover point l (mm)  TA (msec.)                                           ______________________________________                                        1P                30      30                                                  2P                60      300                                                 3P                90      570                                                 4P               120      840                                                 5P               150     1110                                                 6P               180     1380                                                 7P               210     1650                                                 8P               240     1920                                                 9P               270     2190                                                 0P               300     2460                                                 ______________________________________                                    

2-color state 1 (FIG. 30)

In the 2-color state 1, the program flow remains in a waiting stateuntil the timer Tsc-A has timed. When the point Po' on the electrostaticlatent image, which corresponds to the changeover point Po, is justpassing through the area confronting the first developing sleeve 51 uponlapse of the preset time period of the timer Tsc-A, the first developingbias voltage is changed from the color level of -150V to the black levelof -300V at step SC101 and the sleeve solenoid is changed over to theblack mode at step SC102 such that the driving force of the main motoris transmitted to the second developing device 6.

Then, at step SC103, a timer Tsc-B for delaying actuation of the bristleshutter 71 is set. Subsequently, at step SC 104, the 2-color state No.2SN is set to 2 and the program flow returns.

Meanwhile, at the time when the point Po' on the electrostatic latentimage, which corresponds to the color changeover point Po, has passedthrough the area confronting the first developing sleeve 51, a rear edgeportion of the color toner image developed at the first developingdevice 5 does not yet reach an area confronting the second developingdevice 6. Therefore, if the bristle shutter 71 is turned offconcurrently with lapse of the present time period of the timer Tsc-A,the color toner image is disturbed by the magnetic brush formed by thesecond developing sleeve 61. Thus, in order to prevent such aphenomenon, the timer Tsc-B is provided for delaying actuation of thebristle shutter 71. More concretely, supposing that characters T3, T4and T5 denote a time period during which a point on the photosensitivedrum 2 proceeds from the first developing device 5 to the seconddeveloping device 6, a time period during which a point on thedeveloping sleeve 61 proceeds from the bristle shutter 71 to an areaconfronting the photosensitive drum 2 and a time period during which thebristle shutter 71 changes from the ON state to the OFF state,respectively, a preset time period TB of the timer Tsc-B is set asfollows.

    TB=T3-T4-T5

2-color state 2 (FIG. 31)

In the 2-color state 2, if it is found at step SC200 that the timerTsc-B has timed, the bristle shutter 71 is turned off at step SC201 suchthat development can be performed by the second developing device 6.Subsequently, at step SC202, a timer Tsc-C for delaying turning-off ofthe bristle shutter 71 is set. Then, the 2-color state No. 2SN is set to3 at step SC203 and the program flow returns.

A preset time period TC of the timer Tsc-C changes according to theposition of the color changeover point Po and is concretely set as shownin Table 4 below. The preset time period TC is determined such that notonly the bristle shutter 71 is held in the OFF state at least until thenext development of the region R2 by the second developing device 6 iscompleted but a time period of the OFF state of the solenoid 75 fordriving the bristle shutter 71 is set larger than that of the ON stateof the solenoid 75 in order to maintain normal operationalcharacteristics of the solenoid 75 through restriction of production ofheat in the solenoid 75.

Namely, in the copying apparatus 1 of this embodiment, the solenoid 75for driving the bristle shutter 71 is made small in size so as to makethe apparatus compact.

Therefore, in case where continuous multiple copying is executed,cumulated time period of the ON state of the solenoid 75 increasesquantity of heat produced in the solenoid 75 to raise the temperatureand thereby causes reduced performance. As a result, the solenoid 75cannot bear resisting load of the toner impinging on the bristle shutter71 and thus, becomes unable to maintain normal operationalcharacteristics.

Therefore, as shown in FIG. 10, in order to secure a cooling-off periodof the solenoid 75, the preset time period TC is set such that thesolenoid 75 is held at a stop by setting a ratio (duty ratio) R of thetime period Ton to the time period Toff as follows.

    R=Ton/Toff<0.5

                  TABLE 4                                                         ______________________________________                                        Changeover point                                                                              TC (msec.)                                                    ______________________________________                                        1P              5790                                                          2P              6090                                                          3P              6330                                                          4P              6600                                                          5P              6870                                                          6P              7140                                                          7P              7410                                                          8P              7680                                                          9P              7950                                                          0P              8220                                                          ______________________________________                                    

2-color state 3 (FIG. 32)

In the 2-color state 3, the program flow remains in a waiting stateuntil the timer Tsc-C has timed. If it is found at step SC300 that thetimer Tsc-C has timed such that the bristle shutter 71 can be turned on,the 2-color state No. 2SN is set to 0 at step SC301 and the program flowreturns.

(C) ATDC subroutine

Hereinbelow, the ATDC subroutine is described with reference to FIGS. 33to 42 and FIGS. 13 and 14. This subroutine is provided for controllingsecond replenishment of the toner to the developing devices 5 and 6. Atstep SCAA, an ATDC state No. ASN is judged. On the basis of a value ofthe ATDC state No. ASN, the program flow proceeds to one of steps SCA0to SCA9 for ATDC states 0 to 9, respectively. Meanwhile, at the timewhen the power source of the copying apparatus 1 has been turned on, theATDC state No. ASN is set to 0 in the initialization subroutine (stepMl) of the main routine of FIG. 15. Hence, the program flow initiallystarts from the ATDC state 0.

In the case where the black copying mode or the color copying mode isselected in this subroutine, processing is performed by the ATDC states0, 1 and 9. Meanwhile, in the case where the simultaneous color copyingmode is selected, processing is performed by the ATDC states 0 and 2 to8.

Subsequently, after the above-described processing of each state hascompleted, a special black toner replenishment subroutine is performedat step SCA10 and a special color toner replenishment subroutine isperformed at step SCA11.

ATDC state 0 (FIG. 34)

In the ATDC state 0, a decision is made at step SCA000 as to whether ornot the simultaneous color copying mode is selected. If it is found atstep SCA001 that a demand for copying has been detected in thesimultaneous color copying mode, the ATDC state No. ASN is set to 2 atstep SCA002 and the program flow returns. In the case of "NO" at stepSCA001 in the simultaneous color copying mode, the program flow proceedsto step SCA010.

On the other hand, in the case where the copying mode other than thesimultaneous color copying mode, i.e. the black copying mode or thecolor copying mode is selected, a decision is made at step SCA020 as towhether or not scanning has been started. In the case of "YES" at stepSCA020, steps SCA021 to SCA024 are executed and the program flowreturns. In the case of "NO" at step SCA020, the program flow proceedsto step SCA010.

Meanwhile, at step SCA021, an ATDC counter is cleared for itsinitialization and at step SCA022, an ATDC detection timing flag FATDCis set to 1 so as to start an ATDC detection subroutine to be describedlater. Subsequently, at step SCA023, an ATDC detection timer Tat-A forreceiving output signals from the ATDC sensors AS1 and AS2 mounted onthe developing devices 5 and 6, respectively is set. Therefore, during apreset time period T-A of the timer Tat-A, the output signals from theATDC sensors AS1 and AS2 are read and the toner density of thedeveloping devices 5 and 6 is judged as an average of the output signalsof the ATDC sensors AS1 and AS2. Reference should be made to a timingchart of FIG. 14.

Meanwhile, at step SCA010, a decision is made as to whether or not atimer Tat-C or Tat-D for counting a time period for replenishment of thetoner, which is set in the ATDC state 1 to be described later, hastimed. In the case of "YES" at step SCA010, a black toner replenishmentmotor for replenishing the black toner to the developing device 6 fromthe toner replenishment bottle 91 is turned off at step SCA011 and acolor toner replenishment motor for replenishing the color toner to thedeveloping device 5 from the toner replenishment bottle 81 turned off atstep SCA012.

ATDC state 1 (FIG. 35)

The ATDC state 1 is provided for starting second replenishment of thetoner in the black copying mode and the color copying mode. At stepSCA100, a decision is made as to whether or not the above describedtimer Tat-A has timed. In the case of "NO" at step SCA100, program flowreturns. In the case of "YES" at step SCA100, the ATDC detection timingflag FATDC is set to 0 at step SCA101 so as to detect the toner densityand the ATDC state No. ASN is set to 9 at step SCA102.

Then, at step SCA103, a decision is made as to whether the black copyingmode or the color copying mode is selected. In the case where the colorcopying mode is selected, the color toner replenishment motor is turnedon at step SCA104 so as to supply the color toner to the firstdeveloping device 5. Meanwhile, in the case where the black copying modeis selected, the black toner replenishment motor is turned on at stepSCA105 so as to supply the black toner to the second developing device6.

Subsequently, at step SCA106, a decision is made as to whether or not atoner density Tc of each of the developing devices 5 and 6, which hasbeen detected in the ATDC sensor detection subroutine during the presettime period T-A of the timer Tat-A, is larger than a predeterminedreference level To. In the case of "YES" at step SCA106, a first tonerreplenishment timer Tat-C having a preset time period T-C of 180 msec.is set at step SCA107 such that a predetermined amount of the toner isreplenished, that is, first toner replenishment is performed, during thepreset time period T-C as shown by the broken lines in FIG. 14. At stepSCA108, a decision is made as to whether or not the copying mode flagFCOLOR is 1. If the flag FCOLOR is 1 at step SCA108, namely, when thecolor copying mode is selected, a counter flag CNTC is reset to 0 atstep SCA109 and a special color toner replenishment flag FSUPC is resetto 0 at step SCA110. If the copying mode flag FCOLOR is 0 at stepSCA108, a counter flag CNTB is reset to 0 at step SCA111 and a specialblack toner replenishment flag FSUPB is reset to 0 at step SCA112.

Meanwhile, the counter flags CNTC and CNTB are, respectively, providedfor counting how many times a toner density detection value detected ateach one routine time is successively lager than the predeterminedreference level, that is, how many times the second replenishment to bedescribed later is successively performed. The counter CNTC correspondsto the first (color) developing device 5 and the counter CNTBcorresponds to the second (black) developing device 6.

The special color toner replenishment flag FSUPC and the special blacktoner replenishment flag FSUPB respectively are provided for controllinga special (third) toner replenishment operation performing in an extremelot of toner consumption of the first (color) developing device 5 andthe second (black) developing device 6.

Meanwhile, in the case of "NO" at step SCA106, a second tonereplenishment timer Tat-D having a preset time period T-D of 3,990 msec.is set at step SCA113 such that ATDC (second) replenishment of thetoner, whose amount is larger than the amount of the first tonerreplenishment, is performed during the preset time period T-D.

Then, a decision is made at step SCA114 as to whether or not the copyingmode flag FCOLOR is 1.

If the flag FCOLOR is 1 at step SCA114, count of the counter CNTC isincreased at step SCA115. Subsequently, at step SCA116, a decision ismade as to whether or not a counted number of the counter CNTC is lagerthan a predetermined reference value Nc. If the case of "YES" at stepSCA116, the special color toner replenishment flag FSUPC is set to 1 atstep SCA117 and the counter flag CNTC is reset to 0 at step SCA118.Namely, in the case where the toner density does not reach the referencelevel To in spite of usual performance of the second tonerreplenishment, that is, when consumption of toner is extremely large,the operation is changed over from the second toner replenishment stateto the third toner replenishment state.

If the case of "NO" at step SCA114, count of the counter CNTB isincreased at step SCA119. Subsequently, at step SCA120, a decision ismade as to whether or not a counted number of the counter CNTB is lagerthan a predetermined reference value Nb. If the case of "YES" at stepSCA120, the special black toner replenishment flag FSUPB is set to 1 atstep SCA121 and the counter flag CNTB is reset to 0 at step SCA122.

ATDC state 2 (FIG. 36)

The ATDC state 2 is a subroutine to be executed in the case where it hasbeen judged in the ATDC state 0 that the simultaneous color copying modeis selected. At step SCA200, a decision is made as to whether or notcopying is being performed. In the case of "YES" at step SCA200, adecision is made at step SCA201 as to whether or not the simultaneouscolor copying mode is selected and a decision is made at step SCA202 asto whether or not the main motor is in the ON state. In the case of"YES" at not only step SCA201 but step SCA202, the program flow proceedsto step SCA203. Meanwhile, in the case of "NO" at one of steps SCA200 toSCA202, the program flow proceeds to steps SCA220 and SCA221.

Meanwhile, if not only the simultaneous color copying mode is selectedbut also the main motor is in the ON state, a decision is made at stepSCA 203 as to whether or not the second (black) developing sleeve 61 isin operation. In the case of "YES" at step SCA203, the ATDC state No.ASN is set to 3 at step SCA204. In the case of "NO" at step SCA203,namely when the first (color) developing sleeve 51 is in operation, theATDC state No. ASN is set to 6 at step SCA210.

Meanwhile, in the case of "NO" at one of steps SCA200 to SCA202, theATDC detection timing flag FATDC is set to 0 at step SCA200 and the ATDCstate No. ASN is set to 0 at step SCA221.

Subsequently, at step SCA205, a timer Tat-E is set at step SCA205 andthe program flow returns. This timer Tat-E is used for delayingdetection of the toner density until the developer is fully mixed in thedeveloper 5 or 6 after start of operation of the developing device 5 or6.

ATDC states 3 and 6 (FIG. 37)

In the ATDC states 3 and 6, a decision is made at step SCA300 as towhether or not copying is being performed. In the case of "NO" at stepSCA300, the ATDC detection timing flag FATDC is set to 0 at step SC310and the ATDC state No. ASN is set to 0 at step SCA311 and then, theprogram flow returns.

Meanwhile, in the case of "YES" at step SCA300, a decision is made atstep SCA301 as to whether or not the timer Tat-E has timed. In the caseof "NO" at step SCA301, the program flow returns. In the case of "YES"at step SCA301, steps SCA302 to SCA305 are executed and the program flowreturns. At step SCA302, the ATDC counter is cleared and the ATDCdetection timing flag FATDC is set to 1 at step SCA303. Thereafter, atstep SCA304, the timer Tat-A is set. Furthermore, at step SCA305, theATDC state No. ASN is reset to 4 and 7 if the ATDC state No. ASN is 3and 6, respectively.

ATDC state 4 (FIG. 38)

This ATDC state 4 is provided for replenishing the black toner to thesecond (black) developing device 6 during development of the seconddeveloping device 6 in the simultaneous color copying mode. At stepSCA400, a decision is made as to whether or not the above describedtimer Tat-A has timed. In the case of "YES" at step SCA400, the programflow proceeds to step SCA401 at which the ATDC detection timing flagFATDC is set to 0. Then, at step SCA402, the ATDC state No. ASN is setto 5. Subsequently, the black toner replenishment motor is turned on atstep SCA403 and the color toner replenishment motor is turned off atstep SCA404. Thereafter, at step SCA405, a decision is made as towhether or not the toner density Tc in the second (black) developingdevice 6 is larger than the predetermined reference level To. In thecase of "YES" at step SCA405, the first toner replenishment timer Tat-Chaving the preset time period T-C of 180 msec. is started at stepSCA406. Subsequently, the counter flag CNTB is reset to 0 at step SCA407and the special black toner replenishment flag FSUPB is reset to 0 atstep SCA408. Meanwhile, in the case of "NO" at step SCA405, the secondtoner replenishment timer Tat-D having the preset time period T-D of3,990 msec. is started such that the second toner replenishment isstarted. Subsequently, the count of the counter CNTB is increased atstep SCA411 and a decision is made at step SCA412 as to whether or notthe counted number of the counter CNTB is lager than the predeterminedreference value Nb. If the case of "YES" at step SCA412, namely when theconsumption of toner is extremely large, the special black tonerreplenishment flag FSUPB is set to 1 at step SCA413 and the counter CNTBis cleared at step SCA414.

During counting of the timer Tat-A at step SCA400, the program flowproceeds to step SCA420 at which a decision is made as to whether or notcopying is being performed. In the case of "NO" at step SCA420, the ATDCdetection timing flag FATDC is set to 0 at step SCA430 and the ATDCstate No. ASN is set to 0 at step SCA431 and the program flow returns.On the other hand, in the case of "YES" at step SCA420, a decision ismade at step SCA421 as to whether or not the first (color) developingsleeve 51 is in the ON state, namely the black toner has been changedover to the color toner during copying. In the case of "YES" at stepSCA421, the timer Tat-E is set again at step SCA422 and the ATDC stateNo. ASN is set to 6 at step SCA423 and the program flow returns.

ATDC state 5 (FIG. 39)

In the ATDC state 5, at step SCA500, a decision is made as to whether ornot the timer Tat-C or Tat-D set in the above described ATDC state 4 hastimed. In the case of "YES" at step SCA500, the black tonerreplenishment motor and the color toner replenishment motor are,respectively, turned off at steps SCA501 and SCA502 and the program flowreturns such that subsequent processing is controlled by othersubroutines.

On the other hand, in the case of "NO" at step SCA500, a decision ismade at step SCA510 as to whether or not copying is being performed. Inthe case of "NO" at step SCA510, the ATDC detection timing flag FATDC isset to 0 at step SCA520 and the ATDC state No. ASN is set to 0 at stepSCA521 and the program flow returns. Meanwhile, in the case of "YES" atstep SCA510, a decision is made at step 511 as to whether or not thecolor developing sleeve 51 is in the ON state, namely drive has beenchanged over from the black developing sleeve 61 to the color developingsleeve 51. In the case of "YES" at step SCA511, the timer Tat-E is setat step SCA512 and the ATDC state No. ASN is set to 6 at step SCA513 andthe program flow returns.

ATDC state 7 (FIG. 40)

The ATDC state 7 is provided for replenishing the color toner duringdevelopment of the first (color) developing device 5. At step SCA700, adecision is made as to whether or not the timer Tat-A set in the ATDCstate 6 has timed. In the case of "YES" at step SCA700, the program flowproceeds to step SCA701.

At step SCA701, the ATDC detection timing flag FATDC is set to 0 and atstep SCA702, the ATDC state No. ASN is set to 8. Subsequently, the colortoner replenishment motor is turned on at step SCA703 and the blacktoner replenishment motor is turned off at step SCA704. Thereafter, atstep SCA705, a decision is made as to whether or not the toner densityTc in the first (color) developing device 5 is lager than thepredetermined reference level To. In the case of "YES" at step SCA705,the first toner replenishment timer Tat-C having the preset time periodT-C of 180 msec. is started at step SCA706. Subsequently, the counterflag CNTC is reset to 0 at step SCA707 and the special color tonerreplenishment flag FSUPC is reset to 0 at step SCA708. On the otherhand, in the case of "NO" at step SCA705, the second toner replenishmenttimer Tat-D having the preset time period T-D of 3,990 msec. is startedat step SCA710. Subsequently, the count of the counter CNTC is increasedat step SCA711 and a decision is made at step SCA712 as to whether ornot the counted number of the counter CNTC is lager than thepredetermined reference value Nc. If the case of "YES" at step SCA712,namely when the consumption of toner is extremely large, the specialcolor toner replenishment flag FSUPC is set to 1 at step SCA713 and thecounter CNTC is cleared at step SCA714.

Meanwhile, in the case of "NO" at step SCA700, the program flow proceedsto step SCA72 at which a decision is made as to whether or not copyingis being performed. In the case of "NO" at step SCA720, the ATDCdetection timing flag FATDC is set to 0 at step SCA730 and the ATDCstate No. ASN is set to 0 at step SCA731 and the program flow returns.In the case of "YES" at step SCA720, a decision is made at step SCA721as to whether or not the second (black) developing sleeve 61 is in theON state. In the case of "YES" at step SCA721, the ATDC state No. ASN isset to 3 at step SCA722 and the timer Tat-E is set at step SCA723 andthe program flow returns.

ATDC state 8 (FIG. 41)

In the ATDC state 8, a decision is made at step SCA800 as to whether ornot the toner replenishment timer Tat-C or Tat-D set in the abovedescribed ATDC state 7 has timed. In the case of "YES" at step SCA800,the black toner replenishment motor and the color toner replenishmentmotor are, respectively, turned off at steps SCA801 and SCA802 and theprogram flow returns. On the other hand, in the case of "NO" at stepSCA800, a decision is made at step SCA810 as to whether or not thesecond (black) developing sleeve 61 is in the ON state. In the case of"YES" at step SCA810, the timer Tat-E is set at step SCA811 and the ATDCstate No. ASN is set to 3 at step SCA812 and the program flow returns.

ATDC state 9 (FIG. 42)

In the ATDC state 9, a decision is made at step SCA900 as to whether ornot scanning has been completed. In the case of "YES" at step SCA900,the ATDC state No. ASN is set to 0 at step SCA901 and the program flowreturns.

On the other hand, in the case of "NO" at step SCA900, a decision ismade at step SCA910 as to whether or not the timer Tat-C or Tat-D hastimed In the case of "YES" at step SCA910, the black toner replenishmentmotor and the color toner replenishment motor are, respectively, turnedoff at steps SCA911 and SCA912.

Special toner replenishment subroutine

A special black toner replenishment subroutine and a special color tonerreplenishment subroutine are, respectively, provided for speciallyreplenishing toner to the developing device in the case where the numbercounted how many times the toner density Tc, of the developing device,detected at each one routine time in the second toner replenishmentperformance is larger than the predetermined reference level To reachesthe predetermined value Nb or Nc, namely when it is judged that theconsumption of toner is extremely large, in the above-described ATDCstate 1, 4 and 7.

(I) Special black toner replenishment subroutine (FIG. 42A)

In the special black toner replenishment subroutine, a decision is madeat step RSB10 as to whether or not the special black toner replenishmentflag FSUPB is 1. If the case of "YES" at step RSB10, program flowproceeds to step RSB11. If the case of "NO" at step RSB10, program flowreturns. The special black toner replenishment flag FSUPB is set to 1 inthe case where consumption of black toner is extremely large asdescribed above.

Subsequently, at step RSB11, a decision is made as to whether or not astate No. SBSN is 0. The state No. SBSN is set to 0 in the case wherethe power source of the copying apparatus is turned on. If the state No.SBSN is 0 at step RSB11, after a FATDCB flag FATDCB is set to 1 at stepRSB2 so that the signal of the ATDC sensor AS2 is inputted to themicrocomputer, a ATDC counter B for judging a toner density in thespecial black toner replenishment is cleared at step RSB13. Then, atimer Tat-F for defining an input time period (number of times) of theATDC sensor AS2 is started at step RSB14. Drive of the black tonerreplenishment motor is started at step RSB15 so as to start replenishingtoner to the second developing device 6. After that, the state No. SBSNis set to 1 at step RSB16.

Meanwhile, if the state No. SBSN is not 0 at step RSB11, program flowproceeds to step RSB20 and a decision is made at step RSB20 as towhether or not the timer Tat-F started at step RSB14 has timed. If thecase of "NO" at step RSB20, the black toner replenishment is continuedto replenish at step RSB30. If the case of "YES" at step RSB20, theFATDCB flag FATDCB is reset to 0 at step RSB21 so that a signal from theATDC sensor AS2 is not inputted to the microcomputer. Then, a decisionis made at step RSB22 as to whether or not the toner density Tc is largethan the predetermined reference level To. If the case of "NO" at stepRSB22, the black toner replenishment is continued to replenish at stepRSB30. Namely, if the timer Tat-F has timed, the black tonerreplenishment is continued to replenish until the toner density Tc islarge than the reference level To. If the case of "YES" at step RSB22,the toner replenishment is stopped at step RSB23, the special blacktoner replenishment flag FSUPB is reset to 0 at step RSB24 and the stateNo. SBSN is reset to 0 at step RSB25. Then, program flow returns.

(II) Special color toner replenishment subroutine (FIG. 42)

In this special color toner replenishment subroutine, a decision is madeat step RSC10 as to whether or not the special color toner replenishmentflag FSUPC is 1. If the case of "YES" at step RSC10, program flowproceeds to step RSC11. If the case of "NO" at step RSC10, program flowreturns. The special color toner replenishment flag FSUPC is set to 1 inthe case where consumption of color toner is extremely large asdescribed above.

Subsequently, at step RSC11, a decision is made as to whether or not astate No. SCSN is 0. The state No. SCSN is set to 0 in the case wherethe power source of the copying apparatus is turned on. If the state No.SCSN is 0 at step RSC11, after a FATDCC flag FATDCC is set to 1 at stepRSC2 so that the signal of the ATDC sensor AS1 is inputted to themicrocomputer, a ATDC counter C for judging a toner density in thespecial color toner replenishment is cleared at step RSC13. Then, atimer Tat-G for defining an input time period (number of times) of theATDC sensor AS1 is started at step RSC14. Drive of the color tonerreplenishment motor is started at step RSC15 so as to start replenishingtoner to the first developing device 5. After that, the state No. SCSNis set to 1 at step RSC16.

Meanwhile, if the state No. SCSN is not 0 at step RSCll, program flowproceeds to step RSC20 and a decision is made at step RSC20 as towhether or not the timer Tat-G started at step RSC14 has timed. If thecase of "NO" at step RSC20, the color toner replenishment is continuedto replenish at step RSC30. If the case of "YES" at step RSC20, theFATDCC flag FATDCC is reset to 0 at step RSC21 so that a signal from theATDC sensor AS1 is not inputted to the microcomputer. Then, a decisionis made at step RSC22 as to whether or not the toner density Tc is largethan the predetermined reference level To. If the case of "NO" at stepRSC22, the color toner replenishment is continued to replenish at stepRSC30. Namely, if the timer Tat-G has timed, the color tonerreplenishment is continued to replenish until the toner density Tc islarge than the reference level To. If the case of "YES" at step RSC22,the toner replenishment is stopped at step RSC23, the special colortoner replenishment flag FSUPC is reset to 0 at step RSC24 and the stateNo. SCSN is reset to 0 at step RSC25. Then, program flow returns.

(D) ATDC sensor detection subroutine

Hereinbelow, the ATDC sensor detection subroutine is described withreference to FIG. 43. This subroutine is provided for detecting thetoner density Tc on the basis of a signal inputted, during the presettime periods T-A, T-B, T-C of the timers Tat-A, Tat-F, Tat-G, fromeither one of the ATDC sensors AS1 and AS2 in a corresponding one of thefirst and second developing devices 5 and 6 in use.

At step SAT00, a decision is made as to whether or not the ATDCdetection timing flag FATDC is 1, namely the above timers Tat-A Tat-B,Tat-C are, respectively, counting the preset time period. In the case of"YES" at step SAT00, a decision is made at step SAT01 as to whether ornot the output voltage of the ATDC sensor AS1 or AS2 is higher than apredetermined reference voltage. In the case of "YES" at step SAT01,count of the ATDC counter is increased.

More specifically, for example, the timer Tat-A has the preset timeperiod of 330 msec. and a time period for executing one routine of thissubroutine is set to 30 msec. Thus, during the preset time period of thetimer Tat-A, 11 data are sampled and compared with the reference levelrespectively. When the counts of the ATDC counter etc. in the case wherethe toner density is higher than the reference level are 6 or more, itis judged that the each toner density Tc is higher than the referencedensity To.

Meanwhile, if, at step SAT00, it is judged that the ATDC detectiontiming flag FATDC is 0, a decision is made at step SAT10 as to whetheror not the FATDCB flag for controlling special black toner replenishmentis 1. If the case of "YES" at step SAT00, program flow proceeds to stepSCA01. If the case of "NO" at step SAT11, a decision is made as towhether or not the FATDCC flag for controlling special color tonerreplenishment is 1. If the case of "YES" at step SAT11, program flowproceeds to step SAT01. If the case of "NO" at step SAT11, program flowreturns.

(E) Paper feed and transport control subroutine

Hereinbelow, the paper feed and transport control subroutine isdescribed with reference to FIGS. 44 to 47. This subroutine is providedfor controlling feed of the copy paper sheet from the paper feedingmechanism 30 such that the leading edge of the copy paper sheetcoincides with the front edge of the electrostatic latent image formedon the photosensitive drum 2 and corresponding to the image of theoriginal document, for controlling ejection of the copy paper sheethaving the toner image transferred and fixed thereon to the paperdischarge portion 42 and for proceeding to suspend the copying operationso that the paper feed is stopped during the special tonerreplenishment. Hereinbelow, the subroutine thereof is described.

In this subroutine, initially at step SPT00, a paper state No. PSN isjudged. On the basis of a value of the paper state No. PSN, the programflow proceeds to one of steps SPA00 to SPA0n for paper states 0 to n,respectively.

Meanwhile, at the time when the power source of the copying apparatus 1has been turned on, the paper state No. PSN is set to 0 in theinitialization subroutine of the main routine.

Paper state 0 (FIG. 45)

In the paper state 0, if it is found at step SP000 that copying has beenstarted upon depression of the print switch 102, etc., namely, a flagFCPRQU for indicating copying start timing is 1, a decision is made atstep SP001 as to whether or not changeover of the developing sleeve canbe performed. If the case of "YES" at step SP001, program flow proceedsto the following steps. Subsequently, a timer Tp-A is set at step SP002and the paper state No. PSN is set to 1 at step SP003 and then, theprogram flow returns.

Paper state 1 (FIG. 46)

In the paper state 1, it is judged at step SP100 whether or not theabove described timer Tp-A has timed. The program flow remains in awaiting state until the timer Tp-A has timed. When the timer Tp-A hastimed, the paper state No. PSN is set to 2 at step SP101 and the programflow returns.

Paper state 2 (FIG. 47)

This paper state 2 is provided for judging whether or not one of thefirst and second developing devices 5 and 6 is in the special tonerreplenishment state, so that the paper feed is performed in the onlycase where the devices are not in the replenishment state. At stepsSP200 and SP202, the copying mode is judged. Then, a decision is made atsteps SP201 and SP204 as to whether or not it is in the special blacktoner replenishment state. On the other hand, a decision is made at stepSP203 as to whether or not it is in the special color tonerreplenishment state. Then, if the case of "YES" at the above stepsSP201, SP204 and SP203, program flow returns so as to stop feeding thecopy paper sheet during that time period.

Meanwhile, if the case of "NO" at steps SP204 and SP203, it is judged atstep SP205 whether or not bristle regulation has been completed prior tocopying so as to remove the developer from the surface of the developingsleeve 61 of the second (black) developing device 6. In the case of"YES" at step SP205, drive of the paper feeding roller 32b or 33b isstarted at step SP206 so as to permit copying operation and the paperstate No. PSN is set to 3 at step SP207 and then, the program flowreturns.

(F) Peripheral device control subroutine

Hereinbelow, the peripheral device control subroutine is described withreference to FIGS. 48 to 53. This subroutine is provided for controllingthe peripheral devices of the photosensitive drum 2, i.e. the coronacharger 3, the developing bias voltages of the first and seconddeveloping sleeve 51 and 61, the exposure lamp 11 of the optical system0, etc. Initially, at step SDA, a drum state No. DSN is judged. On thebasis of values of the drum state No. DSN, the program flow proceeds tosteps SD0 to SDn for drum states 0 to n, respectively.

Drum state 0 (FIG. 49)

In the drum state 0, it is initially judged at step SD000 whether or notthe copy flag FCOPY is 1 upon depression of the print switch 102. Then,at step SD001, it is judged whether or not drive of the main motor hasbeen changed over to the second (black) developing device 6. In the caseof "YES" at not only step SD000 but step SD001, steps SD002 to SD005 areexecuted. On the other hand, in the case of "NO" at one of steps SD000and SD001, the program flow returns so as to remain in a waiting state.At step SD002, the developing bias voltage is turned on and at stepSD003, the main motor is turned on. Subsequently, at step SD004, a timerTd-A for delaying actuation of the transfer charger 7 is set and thedrum state No. DSN is set to 1 at step SD005.

Drum state 1 (FIG. 50)

In the drum state 1, it is judged at step SD100 whether or not the timerTd-A has timed. In the case of "NO" at step SD100, the program flowreturns so as to remain in a waiting state. Meanwhile, in the case of"YES" at step SD100, the transfer charger 7 is turned on at step SD101,a timer Td-B for delaying start of exposure is set at step SD102, thedrum state No. DSN is set to 2 at step SD103 and the program flowreturns.

Drum state 2 (FIG. 51)

In the drum state 2, it is judged at step SD200 whether or not the abovedescribed timer Td-B has timed. In the case of "NO" at step SD200, theprogram flow returns so as to remain in a waiting state. In the case of"YES" at step SD200, the drum state No. DSN is set to 3 at step SD201.

Drum state 3 (FIG. 52)

This paper state 3 is provided for judging whether or not one of thefirst and second developing devices 5 and 6 is in the special tonerreplenishment state, so that the exposure lamp 11 is turned on in theonly case where the devices are not in the replenishment state. At stepsSD300 and SD302, the copying mode is judged. Then, a decision is made atsteps SD301 and SD304 as to whether or not it is in the special blacktoner replenishment state. On the other hand, a decision is made at stepSD303 as to whether or not it is in the special color tonerreplenishment state. Then, if the case of "YES" at the above stepsSD301, SD304 and SD303, program flow returns so as to remain in awaiting state.

Meanwhile, if the case of "NO" at steps SD304 and SD303, it is judged atstep SD305 whether or not bristle regulation on the surface of thesecond developing sleeve 61 has been completed prior to copying so as toremove the developer from the surface of the developing sleeve 61 of thesecond (black) developing device 6. In the case of "NO" at step SD305,the program flow returns so as to remain in a waiting state. In the caseof "YES" at step SD305, the exposure lamp 11 of the optical system 0 isturned on at step SD306 so as to start copying operation and a timerTd-C for delaying actuation of the corona charger 3 is set at stepSD307. Then, the drum state No. DSN is set to 4 at step SD308 and theprogram flow returns.

Drum state 4 (FIG. 53)

In the drum state 4, it is judged at step SD400 whether or not the abovedescribed timer Td-C has timed. In the case of "NO" at step SD400, theprogram flow returns so as to remain in a waiting state. In the case of"YES" at step SD400, the corona charger 3 is turned on at step SD401 andthe drum state No. DSN is set to 5 at step SD402 and the program flowreturns.

(G) Auto reset subroutine (FIG. 54)

This subroutine is provided for changing over a copy number set mode andan exposure mode to a standard state, namely, for example, executingsuch a process that the copy number is set to 1 and a copy mode ischanged over to a standard copy mode after canceling a special copymode, in turning on of the power source of the copying apparatus,non-operation of various switches and keys on the operating panel 100during a predetermined time period, non-operation of copying during apredetermined time period or turning on of the automatic reset key 103on the operating panel 100.

At step AR01, it is judged whether or not a FON flag is 1. If the caseof "YES" at step AR01, program flow proceeds to step AR02. If the caseof "NO" at step AR01, program flow proceeds to step AR10. The FON flagis provided for setting to 0 in turning on of the power source of thecopying apparatus. Therefore, the program flow proceeds to step AR02 inthe only case where the power switch of the copying apparatus is turnedon. Then, the program flow proceeds to step AR10 in other case.

Subsequently, at step AR02, the FON flag is set to 1 and at step AR03, adecision is made as to whether or not the special black tonerreplenishment flag FSUPB is 0, namely, the special black tonerreplenishment mode is selected. If the case of "YES" at step AR03, thecopying mode flag FCOLOR is reset to 0 at step AR04. If the case of "NO"at step AR03, a decision is made at step AR05 as to whether or not thespecial color toner replenishment mode is selected. If the case of "NO"at step AR05, namely, when the special color toner replenishment isselected, program flow proceeds to step AR04. IF the case of "YES" atstep AR05, the copying mode flag FCOLOR is set to 1. Namely, if thespecial (black or color) toner replenishment mode is selected, thecopying mode flag FCOLOR is reset to 0 at step AR04 and if the specialtoner replenishment mode is not selected, the copying mode flag FCOLORis set to 1 at step AR06.

After predetermined procedures have been completed at steps AR04 andAR06, respectively, other copying modes, that is, the copy number mode,the exposure mode and the special copying mode (for example, bookseparation copying mode) are reset to standard states, respectively.

According to the above-described description, if neither the first norsecond developing devices 5, 6 is in the special toner replenishmentstate, the second developing device 6 having a priority over the firstdeveloping device 5 is initially selected in the case of turning on ofthe power source of copying apparatus and in the case where the timerTac has timed in non-copying operation. Then, if the second developingdevice 6 is in the special toner replenishment state, the firstdeveloping device 5 is automatically selected.

Meanwhile, if it is judged that the FON flag is 1 at step AR01, adecision is made at step AR10 as to whether or not a timer Tac set atstep AR32 to be described later has timed. If the case of "YES" at stepAR10, program flow proceeds to step AR0. If the case of "NO" at stepAR10, or if the timer Tac is not set, program flow proceeds to step AR20at which a decision is made as to whether or not the auto reset key 103on the operating panel 100 has been turned on. If the case of "YES" atstep AR20, program flow proceeds to step AR03. If the case of "NO" atstep AR20, a decision is made at step AR30 as to whether or not all keyson the operating panel 100 have been turned off. If the case of "YES" atstep AR30, a decision is made at step AR31 as to whether or not copyingis being performed. If the case of "NO" at step AR30, program flowproceeds to step AR32 at which the timer Tac is set. Then, program flowreturns. If the case of "YES" at step AR31, program flow proceeds tostep AR32. If the case of "NO" at step AR31, program flow returns.

(H) Developing automatic changeover subroutine (FIG. 55)

The developing automatic changeover subroutine is provided for changingover the developing device to be used to other developing device tocontinue copying operation in the case where it is judged that tonerreplenishment can not perform by usual toner replenishment since tonerconsumption is unusually and extremely large in the ATDC states 1, 4 and7 of the above ATDC control subroutine.

If it is judged that scanning of the copying apparatus has beencompleted at step RDC00, a decision is made at step RDC01 as to whetheror not the special black toner replenishment mode is selected and adecision is made at step RDC10 as to whether or not the special colortoner replenishment mode is selected. If the special black tonerreplenishment mode is selected, program flow proceeds to step RDC02. Ifthe special color toner replenishment mode is selected, program flowproceeds to step RDC11. If neither the special black toner replenishmentmode nor the special color toner replenishment mode is selected, programflow returns.

If the special black toner replenishment mode is selected, decisions aremade at steps RDC02, RDC03 and RDC04 as to whether or not thesimultaneous copying mode is selected, the toner color accommodated intothe first developing device 5 is same as that accommodated into thesecond developing device 6, and the density Tc of toner into the firstdeveloping device 5 is higher than the reference level To, respectively.If the case of "YES" at steps RDC02, RDC03 and RDC04, the copying modeflag FCOLOR is set to 1 at step RDC05. Namely, the copying mode ischanged over to a copying state where the first developing device 5 isused. If the case of "NO" at one of steps RDC02, RDC03 and RDC04,program flow proceeds returns.

Similarly, if the special color toner replenishment mode is selected,decisions are made at steps RDC11, RDC12 and RDC13 as to whether or notthe simultaneous copying mode is selected, the toner color accommodatedinto the first developing device 5 is same as that accommodated into thesecond developing device 6, and the density Tc of toner into the seconddeveloping device 6 is higher than the reference level To, respectively.If the case of "YES" at steps RDC11, RDC12 and RDC13, the copying modeflag FCOLOR is set to 1 at step RDC14. Namely, the copying mode ischanged over to a copying state where the second developing device 6 isused. If the case of "NO" at one of steps RDCll, RDC12 and RDC13,program flow proceeds returns.

Therefore, when other copying mode than the simultaneous copying mode isselected, if the density of toner into the first or second developingdevice is not higher than the reference level in spite of replenishmentof toner to the first or second developing device, the developing devicein using is changed over to other developing device.

It should be noted here that, in the above-described description, if thecolor toner is accommodated into the first developing device 5 and theblack toner is accommodated into the second developing device 6, even ifthe developing device is in the special toner replenishment state, thedeveloping device in using is not changed over to other device. If thecolor of toner accommodated into the first and second developing devices5 and 6 is same, even if the density of toner into either one of theboth developing devices 5 and 6 is lower than the reference level, theother developing device whose toner density is not lower can use tocontinue copying operation.

As is seen from the above description, according to the embodiment ofthe present invention, in the case where documents having images withmuch solid portion are continuously copied, even if density of toneraccommodated into the developing device in using is lower than thedetermined reference level, the images is continuously developed by theother developing device having the same color toner as the toner in thedeveloping device using. Therefore, in the apparatus, waiting timeperiod is less than before and many documents can be copied in a shorttime while keeping images of copied papers in good quality.

Furthermore, when the plurality of developing devices have an order ofpriority respectively and the developing device having higher order ofpriority is in an unsuitable state for development, the device to beused is changed over from the developing device in using to otherdeveloping device having lower order of priority. Therefore, a copiedimage in good quality is continuously obtained.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to be notedhere that various changes and modifications will be apparent to thoseskilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention, theyshould be construed as being included therein.

It is to be noted here that, for example, in the copying apparatus,although it is described that ATDC sensors AS1 and AS2 are,respectively, provided for the first and second developing devices 5 and6 to detect the density of toner into the developing devices in theabove embodiment, this invention can be applied to such system that areference latent image formed on the surface of the photosensitive drum2 is developed into a visible image by the developing devices 5 and 6,so as to detect the toner density thereof. Such system is called anautomatic image density control (AIDC). If the system is applied in thecopying apparatus and the apparatus is constructed such that one tonerdensity detection is performed in one copying operation, it becomespossible to prevent from unnecessary drop of toner density byapplication of the present invention.

Furthermore, it is to be noted that if the above-described copyingapparatus has means for including such function that copying operationis resumed when the print switch 102 is turned on during the specialtoner replenishment mode and during stop of copying, copied image on thecopying paper sheet is quickly obtained in spite of lower density oftoner.

It is also to be noted that, according to the present invention, thecopying apparatus can be constructed such that even if number counteddrop of toner density reaches a predetermined value, in the case wherethe remain number in the number of documents to be successively copiedis lower than a specified value, or where the replenishment has beenperformed longer than at least a specified time period, at that time,copying operation can be started.

It is further to be noted that, in the copying apparatus, the copyingapparatus has a selection key for selecting the special tonerreplenishment and an operator can be depressed the key so as toreplenish toner by his judgment when the toner density of a copied imageon a copied paper drops.

It is to be noted that in the copying apparatus, when toner density indeveloper does not reach the predetermined value in spite of sufficientrotation of the toner replenishment motor, it can be judged that thetoner replenishment bottles 81 and 91 are empty. Therefore, the copyingapparatus can be constructed such that, in such case, tonerreplenishment is stopped and toner empty state is displayed.

What is claimed is:
 1. An image forming apparatus in which anelectrostatic latent image formed on a photosensitive member isdeveloped by a developer incorporating toner and carrier andsubsequently transferred to a paper, the apparatus comprising:first andsecond developing means selectively operable for developing theelectrostatic latent image by first and second developers, respectively;toner accommodating means for accommodating toner to be replenished toeach of the developers; detecting means for detecting toner density ineach of the developers; judging means for judging whether the first andsecond developers have same color; selecting means responsive to saiddetecting means and judging means for automatically selecting saidsecond developing means in the case where the toner density in the firstdeveloper is less than a specified value and where the toner density inthe second developer is not less than the specified value under thejudgment by said judging means that the first and second developers havesame color; replenishing means for replenishing toner to each of thefirst and second developers; and means for activating said replenishingmeans so as to continuously replenish toner to the first developer untilthe toner density therein reaches the specified value in the case whereboth of the toner density in the first and second developers are lessthan the specified value even if the first and second developers havesame color, while prohibiting an image forming operation.
 2. A imageforming apparatus as claimed in claim 1, wherein each of said first andsecond developing means is detachably provided in a main body of theapparatus.
 3. An image forming apparatus as claimed in claim 1, whereinsaid detecting means detects the toner density in each of the first andsecond developers every image forming operation.
 4. An image formingapparatus as claimed in claim 1, wherein each of said first and seconddeveloping means is provided with said detecting means.
 5. An imageforming apparatus as claimed in claim 2, wherein said judging meansincludes color representing means provided in said developing means forrepresenting color of the developer accommodated thereinto and meansprovided in the main body for detecting the color represented by saidcolor representing means.
 6. An image forming apparatus in which anelectrostatic latent image formed on a photosensitive member isdeveloped by a developer incorporating toner and carrier andsubsequently transferred to a paper, the apparatus comprising:first andsecond developing means selectively operable for developing theelectrostatic latent image by first and second developers, respectively;toner accommodating means for accommodating toner to be replenished toeach of the developers; detecting means for detecting toner density ineach of the developers every image forming operation; first replenishingmeans responsive to said detecting means for replenishing apredetermined amount of toner from said respective toner accommodatingmeans to the respective developer when the toner density detected bysaid detecting means is less than the specified value; means forcounting the continuous number of replenishment by said firstreplenishing means; second replenishing means responsive to saidcounting means for continuously replenishing toner from said toneraccommodating means to the respective developer until the toner densityreaches the specified value when the continuous number of replenishmentby said second replenishing means becomes a predetermined number; andmeans for prohibiting an image forming operation during replenishment bysaid second replenishing means.
 7. An image forming apparatus as claimedin claim 6, wherein each of said first and second developing means isprovided with said detecting means.
 8. An image forming apparatus asclaimed in claim 6, wherein said judging means includes colorrepresenting means provided in said developing means for representingcolor of the developer accommodated thereinto and means provided in themain body for detecting the color represented by said color representingmeans.
 9. An image forming apparatus in which an electrostatic latentimage formed on a photosensitive member is developed by a developerincorporating toner and carrier and subsequently transferred to a paper,the apparatus comprising:first and second developing means selectivelyoperable for developing the electrostatic latent image by first andsecond developers, respectively; toner accommodating means foraccommodating toner to be replenished to each of the developers;detecting means for detecting toner density in each of the developersevery image forming operation; first replenishing means for replenishinga first predetermined amount of toner to the respective developer whenthe toner density detected by said detecting means is not less than aspecified value; second replenishing means responsive to said detectingmeans for replenishing a second predetermined amount of toner more thansaid first one to the respective developer when the toner densitydetected by said detecting means is less than the specified value; meansfor counting the continuous number of replenishment by said secondreplenishing means; third replenishing means responsive to said countingmeans for continuously replenishing toner to the respective developeruntil the toner density reaches the specified value when the continuousnumber of replenishment by said second replenishing means becomes apredetermined number; judging means for judging whether the first andsecond developers have same color; selecting means responsive to saiddetecting means, counting means and judging means for automaticallyselecting said second developing means in the case where the continuousnumber of replenishment to the first developer by said secondreplenishing means becomes the predetermined number and where the tonerdensity in the second developer is not less than the specified valueunder the judgment by said judging means that the first and seconddevelopers have same color; and means responsive to said detectingmeans, counting means and judging means or prohibiting an image formingoperation during replenishment to the first developer by said thirdreplenishing means in the case where the continuous number ofreplenishment to the first developer by said second replenishing meansbecomes the predetermined number and where the toner density in thesecond developer is not less than the specified value even if the firstand second developers have same color.
 10. An image forming apparatus asclaimed in claim 9, wherein each of said first and second developingmeans is provided with said detecting means.
 11. An image formingapparatus as claimed in claim 9, wherein said judging means includescolor representing means provided in said developing means forrepresenting color of the developer accommodated thereinto and meansprovided in the main body for detecting the color represented by saidcolor representing means.